Burning rate acceleration catalysts for solid propellant compositions



United States Patent BURNING RATE ACCELERATION CATALYSTS FOR SOLID PROPELLAN'E COMPOSITIONS Ralph W. Lawrence, Glendora, Calif., assignor to Aerojet-General Corporation, Azusa, Calif.,. a corporation of Ohio No Drawing. Filed May 13,1955,- Ser. No. 508,314 19 Claims. (Cl. 60-354) This invention relates to a new burning rateaeceleration catalyst for solid propellant compositions.

Solid, non-metallic propellant compositions are used for rocket and ordnance projection, as well as for assisted aircraft take-offsv Such propellant compositions are composed essentially of two main components; namely, a combustible organic resin fuel and an oxidizing inaterial. In use, such propellants are enclosed within a chamber and ignited whereby large quantities of gases are formed. These gases are exhausted through 'an orifice thereby giving propulsive force to the vehicle in the opposite direction.

The fuel component of the propellant needs only to be combustible and possess physical properties which permit it to be cast or molded into a propellant grain. ..,A wide variety of resins, such as -asphalt,.polyesters, polyalcohols, polynitroalkenes, andmixtures thereof, are useful for this purpose.

The oxidizing material is usually an inorganic oxidizing salt. Metal salts, such as potassium perchlorate, are often used; however, upon combustion they foim solid particles which create large quantifies of visible smoke. Smoke is highly undesirable for military purposes of concealment. Metallic salts useful. in such formulations are considerably more expensive than the corresponding ammonium salts. Hence, non-smoking, non-metallic,'inorganic oxidizing salts-such as hydrazine and ammonium salts are preferred in such applications.v

The desirability of rapid burning propellants for rocket and ordnance. projections is well, established. Metalcontai-ning oxidizers generally .providefastbu'rning compositions. Unfortunately, propellants utilizing the inexpensive, non-met-allic, inorganic oxidizing salts as the oxidizer have heretofore exhibited only relatively slow burning rates. For example, ammonium nitrate oxidized propellants have never been known to at rates in excess of 0.10 in./sec., even though combusted in the presence of burning rate acceleration catalysts such as ammonium dichromate. A i i I have now found that the burning rates of the highly desirable non-metallic propellants can be increased as much as 100% by incorporating small amounts: of lead chloride in the formulation. Lead chloride is-used-in the compositions in such small amounts,'usual1y from about 0.05% to about 5% by weight of the composition, that the smoke formed by its combustion is negligible. The catalyst of this invention is particularlfvaluabl'e when employed in combination with convehtionalxburning rate acceleration catalysts such as ammonium dichromate; however, its' use is not limited tothis particular embodiment of the invention.

Oxidizers useful in the practice of this invention are nonmetallic chlorate, perchlorate, and nitrate salts such as ammonium nitrate, ammonium-chlorate, ammonium perchlorate and hydrazine nitrate; The-non-metallic nitrate salts are preferred: due" to availability; stability and the ease with which they can be handled; The nitrate salts, however, usually do not burn as rapidly as the chlorate or perchlorate-salts;

The oxidizer, im a finely divided condition, is dispersed throughout the fuel component of the'propellant.v .Ql'dl- :formamide and N,N-dimethyl vinyl carbamate.

3,000,175. Patented Sept. 19, 1961 narily, the oxidizer is present in an amount of from about 45% to about by weight of the total composition. Optimum results are obtained when there is suliicient oxygen in the propellant to oxidize all of the carbon in the fuel to carbon monoxide and one-third of the hydrogen to water.

Combustible organic resinous fuels useful in propellant compositions of this invention include: asphalt, polymers and copolymers of alkenes, arylalkenes, alkynes, alkenyl diglycols, alkyl alkenoates, alkenyl alkanoates, alkenoamides, and amido alkenyls, and unsaturated alkyd resins heteropolymerized with the above compounds.

Asphalts having softening points of about180 F. to about 220 F., and penetration values of about 7 to 9 mm./5 see/ gm. at a temperature of 720 F., are usually preferred for rocket fuel due to their ballistic properties. -When castability and low expansion coefficien'ts are not essential, other grades of asphalt can be used. To improve the physical properties of the asphalt,

a condensation product of sebacic acid and a poly-hydric Propellam composition .4

Percent Ammonium perchlorate 75.0 Asphalt 10.5 Cetyl' .acetamid'e 3.0 Castor 7 8.0 Dibutyl seb 3.5

The asphalt-base propellant grains are prepared .by heating the asphalt untilsoft, ordinarilyabout350 F.,

stirring. inzthe oxidizers and additives, andthen permitting the mixture to harden in a mold. I

Polyalkenoamides and amidoalkenyls useful as fuels include: N,N-dimethyl 'acrylamide, N-methyl aci'ylamide, N-nitro'-N=methyl acrylarru'de, 'acrylami'de' N,N -dially1 Suitable fuelsfof this type 'aremore fully disclosed assignees copending application Serial No. 392,472, filed November 16, 1953. Atypical formulationof a propellant compositionghaving a polyamide fuel component is as follows:

Propellant composition B Y Percent Ammonium nitra V 76.81 N,N-dimethyl acrylamide 22.94

.Methyl .amyl;ketone peroxide (polymerizationcatalyst). 0.25

The polyamide propellant grain can be preparedby mixing the amide, oxidizer and polymerization catalyst until a homogeneous mixture is obtained and curing the mixture at a temperature of from about 25 C. to about l-00.- C'.

Bolyalkenes useful as fuels are:. polyisobutylene, butadiene-styrene copolymers, butadiene-acrylonitrile copolymers, and isobutylene-isoprene copolymers: Suitable fuels of this type are more" fully disclosed iniassignees 3 copending application Serial No. 637,004, filed December 22, 1945.

A typical formulation of a propellant composition having a polyolefinic fuel component is as follows:

Propellant composition C Percent Ammonium perchlorate 7 6.0

Copolymer 24.0

Isobutylene 98.5 Isoprene 1.5%

The polyolefin-base propellant grain can be prepared by roll milling the oxidizer into the polyolefin until a homogeneous mixture is obtained and then pressing the material into sheets or discs.

Polyalkenoates useful as fuels include: polymers and copolymers of acrylic acid, acrylic acid esters, methacrylic acid and methacrylic acid esters. Suitable fuels of this type are more fully disclosed in assignees copending application Serial No. 321,943, filed November 21, 1952, now abandoned. A typical formulation of a propellant composition having a polyester fuel component is as follows:

Propellant composition D Percent Hydrazine nitrat 60.00 Methyl acrylate 25.60 Allyl diglycol carbonate 3.60 Methyl methacrylate 10.40 t-Butyl peroxide (polymerization catalyst) 0.40

The polyester-base propellant grain is prepared by mixing the various monomers, oxidizer and polymerization catalyst until a homogeneousmixture is obtained, and then curing the mixture in a mold.

Alkyd resin fuels are usually polyesters prepared by the condensation of a polycarboxylic acid with a polyhydric alcohol, one or both of which contain olefinic linkages. Among the unsaturated polycarboxylic acids which are ordinarily used in the preparation of such polyesters are maleic, fumaric, citraconic, mesaconic, itaconic acids, etc. Saturated acids found to be useful are such acids as oxalic, malonic, succinic and glutaric, etc. The polyhydric alcohols useful are dihydric alcohols such as ethylene glycol, propylene glycol, glycol, etc.; as well as trihydric alcohols such as glycerol; tetrahydric alcohols such as the erythritols; pentahydric alcohols such as arabitol, etc.; or mixtures of any of these alcohols.

The olefinic component of the fuel can be, for example, styrene, vinyl acetate, acrylic acid esters, methacrylic acid esters, allyl compounds such as allyl diglycol carbonate, diallyl maleate, diallyl glycolate, and other olefinic components such as propylene and butadiene, as well as the acetylenes. In general, any unsaturated compound compatible with the resin, and which will polymerize with it, is suitable; this includes all unsubstituted olefins and, in addition, many substituted olefins. Suitable fuels of this type are more fully disclosed in assignees copending application Serial No. 109,409, filed August 9, 1949.

-A typical formulation of a propellant composition utilizing an alkyd resin fuel is as follows:

Propellant composition E Percent Ammonium dichromate 1.99 Ammonium nitrate 72.79 Polyester, by wt. percent 9.79

43.00% diethylene glycol 44.25% adipic acid 1.75% maleic anhydride The alkyd resin-base propellant grains are prepared by blending together the polyester and olefinic components of the fuel, the oxidizer and the burning rate acceleration catalyst. If desired, a polymerization catalyst can also be added. This mixture is cast into a mold and the fuel allowed to heteropolymerize at a temperature in the range of from about 25 C. to about C., and preferably at a temperature below 60 C.

The polymerization catalysts usually employed in such propellant compositions are organic peroxides such as benzoyl peroxide, lauryl peroxide, acetobenzoyl peroxide, ditertiary butyl peroxide, methyl ethyl ketone peroxide, l-hydroxy-cyclohexyl hydroperoxide, cumene hydroperoxide, and cycloalkane hydrocarbon peroxide, and peresters such as tertiary butyl perbenzoate and diperphthalate.

Various other ingredients can also be added for specific purposes without departing from the scope of the invention. For example, lecithin can be added to improve the castability of the uncured propellant. t-Butyl catechol or cobalt 2-ethyl hexanoate is often added as a polymerization modifier.

The propellant grains prepared in the above described manner can withstand rough handling and will perform satisfactorily at temperatures in the range of from about 65 F. to about F.

The particular fuel employed in the propellant composition does not affect the function of the burning rate acceleration catalyst of this invention. In addition to the propellant compositions described above, this catalyst can be used in compositions utilizing fuel components such as polymers of nitroalkenes, nitroalkynes, nitro-containing acids and their esters, as well as other combustible organic polymeric materials.

The burning rate acceleration catalyst herein described is usually incorporated into the propellant compositions in finely divided form and is mixed with the fuel usually at the same time the oxidizer is mixed. To illustrate the improvement in the burning rate brought about by incorporating this catalyst into a solid propellant, the results of a series of burning tests are shown in Table I. These tests were made using propellants E and F described above. In the absence of a catalyst, propellant B does not readily sustain combustion, therefore, as a matter of convenience in establishing a burning rate standard for comparative purposes, ammonium dichromate was incorporated in all of the sample grains. It is to be understood that these examples are presented merely as a means of illustration and are not intended to limit the scope of the invention in any way.

As can be seen from the data presented in Table I, a substantial increase in the burning rate of the propellant was effected by the catalyst of this invention. Increases in burning rate of the magnitude herein obtained are particularly valuable in rocketry and ordnance projection, for such projectiles are ordinaril'y guided only during the period of their launching. When the' full thrust. created by the propellant is available during this time, the projectile can be more effectively directed.

Due to the great increase in the burning rates of nonmetallic, smokeless propellant compositions induced by the above catalyst, and its applicability to propellants having a wide variety of fuel components, it is apparent that this catalyst will find extended and valuable use in the field of rocketry and ordnance propulsion.

I claim:

1. In a method of producing thrust for propulsion by burning a propellant composition, in a chamber wherein said propellant composition consists essentially of a cured intimate mixture of a solid inorganic oxidizing salt and a combustible organic resin, the improvement which comprises burning said propellant in the presence of the burning rate acceleration catalyst, lead chloride.

2. A solid, smokeless, propellant composition comprising a cured intimate mixture of from about 45% to about 90% by weight solid, non-metallic, inorganic, oxidizing salt, from about toabout 35 by weight combustible organic resin, and the burning rate acceleration catalyst lead chloride.

3. The composition of claim 2 wherein the burning rate acceleration catalyst is present in an amount of from about 0.05% to about 5.0% by weight of the total propellant composition.

4. The composition of claim 2 wherein the combustible, organic resin is asphalt.

5. The composition of claim 2 wherein the combustible, organic resin is an olefinic polymer.

6. The composition of claim 2 wherein the combustible, organic resin is alkyl alkenoate heteropolymerized with an olefin.

7. The composition of claim 2 wherein the combustible, organic resin is an unsaturated polyester resin consisting of the condensation product of a saturated polyhydric alcohol and polycarboxylic acid heteropolymerized with an unsaturated compound selected from the group consisting of lower alkenes, lower alkynes, phenyl substituted lower alkenes, lower alkyl dienes, lower alkenyl esters of lower alkanoic acids, lower alkyl esters of alkenoic acids, lower alkenyl esters of lower alkenoic acids, allyl diglycol carbonate, diallyl diglycolate, lower alkenoamide and mixtures thereof; and the burning rate acceleration catalyst, lead chloride.

8. The composition of claim 2 wherein the combustible, organic resin is an alkenoamide polymer.

9. The composition of claim 2 wherein the non-metallic, inorganic, oxidizing salt is selected from the group consisting of nitrate, perchlorate, and chlorate salts of ammonia and hydrazine.

10. A solid, smokeless, propellant composition comprising a cured intimate mixture of from about 45 to about 90% by weight solid, non-metallic, inorganic oxidizing salt, from about 10% to about 35% by weight combustible, organic resin selected from the group con- 6 sisting .of asphalt, polymers and copolymers oi alkenes; arylalken'es, alkadienes, alk'ynes, alkyl ialkenoates, alkenyl alkanoates, alkenyl polyglycols, and unsaturated akyd resins heteropolymerized with the abovepolymerizable compounds, and mixtures thereof, and the burning rate acceleration catalyst, leaduchloride. Y

Th c mposi i n of claim lOHWh ein .theburning rate acceleration catalyst is present in an amountof from about 0.05% to about 5.0% .by weight of the total propellant composition.

12. A so1id, smokeless propellant composition con sisting of a cured intimate mixture of from about 45 to about by weight solid, inorganic, non-metallic, oxidizing salt, from about 10% to about 35% by weight polyester resin consistingof the condensation product of a saturated polyhydric alcoholand polycarboxylic acid heteropolymerized witha lower alkyl alkenoate, and from bout 0.05% to bou -0% by we ht of he t a pro: pellant composition of the burning rate acceleration catalyst, lead chloride.

13. A solid, smokeless, propellant composition comprising a cured intimate mixture of from about 45 to about 90% by weight ammonium nitrate; a fuel component in an amount of from about 10% to about 35 by weight comprising an unsaturated polyester resin consisting of the condensation product of diethylene glycol, adipic acid, and maleic anhydride heteropolymerized with a mixture of styrene and methyl acrylate; ammonium dichromate; and from about 0.05 to about 5.0% by weight of the total propellant composition of the burning rate acceleration catalyst, lead chloride.

14. A solid, smokeless, propellant composition comprising a cured intimate mixture of from about 45 to about 90% by weight ammonium nitrate, from about 10% to about 35% by weight polymeric N,N-dimethyl acrylamide resin, and from about 0.05% to about 5.0% by weight of the total propellant composition of the buming rate acceleration catalyst, lead chloride.

15. A solid, smokeless, propellant composition comprising a cured intimate mixture of from about 45% to about 90% by weight ammonium perchlorate, from about 10% to about 35 by weight resinous isobutylene-isoprene copolymer, and from about 0.05 to about 5.0% by weight of the total propellant composition of the burning rate acceleration catalyst, lead chloride.

16. A solid, smokeless, propellant composition comprising a cured intimate mixture of from about 45 to about 90% by weight hydrazine nitrate, from about 10% to about 35 by weight polyester resin consisting of a mixture of methyl acrylate and methyl methacrylate heteropolymerized with allyl-diglycol carbonate, and from about 0.05 to about 5.0% by weight of the total propellant composition of the burning rate acceleration catalyst, lead chloride.

17. A solid, smokeless, propellant composition com prising a cured intimate mixture of from about 45% to about 90% by weight ammonium perchlorate, from about 10% to about 35 by weight asphalt, and from about 0.05 to about 5.0% by weight of the total propellant composition of the burning rate acceleration catalyst,

'7 acrylamide, acrylamide, N,N-diallyl formamide, N,N dimethyl vinyl carbamate and mixtures thereof;

(0) a rubbery polymer selected from the group consisting of polyisobutylene, butadiene-styrene copolymers, butadiene-acrylonitrile copolymers, isobutylene isoprene copolymers and mixtures thereof;

(d) the addition polymerization product of monomer selected from the group consisting of acrylic acid, acrylic acid esters, methacrylic acid and methacrylic acid esters and mixtures thereof;

(e) heteropolymerized alkyd resins selected from the group consisting of unsaturated polyesters which are the condensation product of polycarboxylic acid and polyhydric alcohol heteropolymerized with phenyl alkenes, lower alkenyl alkanoates, lower alkyl alkenoates, lower alkenyl alkenoates, allyl diglycol carbonate, di-lower alkenyl esters of lower alkendioic acids, dially diglycollate, lower alkenes, lower alkadienes, lower alkynes and mixtures thereof; 7

and from about 0.5% to about 5.0% by weight of the total propellant composition of lead chloride.

19. In a method for producing thrust for propulsion by burning a propellant composition in the combustion chamber of a rocket wherein said propellant composition consists essentially of a cured intimate mixture of a solid inorganic oxidizing salt and a combustible organic resin, the improvement which comprises burning said propellant in the presence of from about 0.05% to about 5.0% by weight of the total propellant composition of the burning rate acceleration catalyst, lead chloride.

References Cited in the file of this patent FOREIGN PATENTS 

1. IN A METHOD OF PRODUCING THUS FOR PROPULSION BY SAID PROPELLANT COMPOSITION, IN A CHAMBER WHEREIN SAID PROPELLANT COMPOSITION CONSISTS ESSENTIALLY OF A CURED INTIMATE MIXTURE OF A SOLID INORGANIC OXIDIZING SALT AND A COMBUSTIBLE ORGANIC RESIN, THE IMPROVEMENT WITH COMPRISES BURNING SAID PROPELLANT IN THE PRESENCE OF THE BURN ING RATE ACCELERATION CATALYST, LEAD CHLORIDE. 